1. Field of the Invention
The present invention relates to a router provided in a mobile communication network and a mobile communication terminal which communicates with said router. Moreover, the present invention also relates to a mobile communication network system having a plurality of routers, and a communication method for the mobile communication network system.
2. Description of the Related Art
In recent years, mobile communication terminals (portable terminals) such as cellular phones, car telephones, Personal Digital Assistants (PDA), and the like, have become widespread, and the use of mobile communication services using such terminals has increased rapidly.
Moreover, the technology for providing mobile communication services is transferring from second-generation mobile communication systems, such as GSM, GPRS, PDC, PDC-P, and the like, or PHS systems, to third-generation mobile communication systems, such as IMT-2000, or small-scale radio access technology, such as wireless LAN, Bluetooth, and the like. Furthermore, investigation has started into an ‘e-Japan’ strategy for moving the technology for providing mobile communication services on further to the establishment of fourth-generation mobile communication technology that can realize a higher speed than IMT-2000.
By providing a plurality of mobile communication environments of different types in this way, the user is able to select the access network most suited to the user's (mobile communications terminal's) location, and the services that he or she wishes to use, so that mobile communication services can be used in a seamless fashion at any time and in any location.
These mobile communication environments are centred on the Internet, which provides high-speed, high-capacity communications, and are realized by means of the high-speed wireless Internet constituted by connecting a variety of wireless access networks to the Internet. Mobile IP is considered to be one of the key technologies in this high-speed wireless Internet.
“Mobile IP” is a protocol which allows communications to be performed in an IP network, whilst the mobile communication terminal changes its connection position on the network, and this protocol was standardized in RFC (Request For Comments) 2002 of the U.S. standardization body IETF (Internet Engineering Task Force).
On the other hand, with the rapid increase in the number of terminals present on IP networks in recent years, the problem of IP address depletion has aggravated. Therefore, the shift to networks using IPv6 which permits use of a larger number of IP addresses swings into full gear. Along with this, the standardization of mobile IPv6 as a protocol which supports movement of terminals on an IPv6 network, in place of mobile IP for an IPv4 network, is progressing, and the IETF is currently investigating RFC publication of same.
The basic mechanism of mobile IP and mobile IPv6 is the same, and therefore the prior art is described below taking mobile IPv6 as an example.
FIG. 8 shows the schematic configuration of an IPv6 network system. The IPv6 network system has a home network 100, Internet core network 200, and access networks 300 and 400.
The home network 100 is an IPv6 network to which a mobile communication terminal (mobile node, hereinafter called “MN”) 500 is connected constantly (by wireless connection), and this communication network is owned and managed, for example, by the carrier (telecommunication operator, and particularly, primary telecommunication operator) to which the MN 500 is subscribed. The home network 100 has a home agent (hereinafter, “HA”) 110 which is a movement management agent.
The access networks 300 and 400 are IPv6 networks owned and managed by a different carrier which is also capable of accommodating the MN 500. The access network 300 has routers 310 and 320, and the access network 400 has routers 410 and 420.
The Internet core network 200 is an IPv6 network, which is constituted by IPv6 routers (not illustrated). The home network 100, and the access networks 300 and 400 are connected to the Internet core network 200, and are able to communicate mutually via the Internet core network 200.
The MN 500 is usually connected to the home network 100 and performs radio communications therewith, and it also has a radio interface for communicating with the access network 300 (router 310 or 320) and access network 400 (router 410 or 420). Consequently, if the MN 500 moves outside the access area of the home network 100, and moves into the access area of the access network 300 or 400, then it performs radio communications with the access network 300 or 400, and accesses the HA 110 of the home network 100 by means of the Internet core network 200.
In this IPv6 network system, if the MN 500 moves from the access area of the home network 100 into the access area of the access network 300 (for example, the access area of router 320) (P1), then the MN 500 starts to connect to the access network 300, and establishes a radio connection with the router 320 (P2).
Thereupon, the MN 500 receives a router advertisement message transmitted by the router 320 (P3). The MN 500 detects that the network prefix (for example, (20::/64)) contained in the router advertisement message thus received is different from the network prefix (for example, (10::/64)) of the home network 100, and thus recognizes that it has left the home network 100.
Next, the MN 500 sends a registration message (hereinafter, called “BU” (Binding Update)), to the HA 110 of the home network 100, via the access network 300 and the Internet core network 200 (P4). This BU contains the home address (the IP address of the MN 500 in the home network 100, for example, (10::10)), and a care-of address (hereinafter, called “CoA”) (for example, (20::10)). The CoA may be assigned to the MN 500 by the router 320 of the access network 300 or by an address allocation router, or it may be generated by the MN 500.
Upon receiving the BU, the HA 110 holds the relationship between the home address and CoA of the MN 500 for a prescribed period of time, as a binding cache (P5).
During the existence of the binding cache, packets (IPv6 packets) sent to the home address of the MN 500 are received by the HA 110, and then forwarded to the CoA of the MN 500. By means of this processing, the MN 500 is able to perform communications even when it moves about on the IPv6 network system.
This management of movement by mobile IPv6 is executed independently in the IPv6 layer by means of an extended header of the IPv6 packet or an extension to the ICMPv6 message, or the like, irrespectively of the type of lower physical layer or data link layer. This means that whatever the type of access network used by the MN 500, it is able to move about on the IPv6 network system.
Therefore, as described above, mobile IPv6 is excellently suitable as a technology for achieving a mobile environment which permits communications services to be used seamlessly, at any time and in any location.
However, with mobile IPv6 problems of the following kind arise when the MN 500 performs handover between different access networks.
The first problem is that during handover, there is a risk that packets will not be transmitted from the HA 110 to the MN 500, and hence packet loss will arise. This problem arises in the following manner.
Namely, if the MN 500 moves from the access area of the access network 300 to the access area of the access network 400 (P6), then according to this movement, the radio signal from the router 320 gradually becomes insufficient, and the connection with the access network 300 is disconnected.
On the other hand, the MN 500 starts connection with the access network 400 (for example, the router 410), and establishes connection therewith (P7). Thereby, the MN 500 receives the router advertisement message sent by the router 410 (P8).
The MN 500 detects that the network prefix contained in the router advertisement message thus received (for example, (30::/64)) is different to both the network prefix (10::/64) of the home network 100 and the network prefix (20::/64) of the access network 200, and hence it recognizes that it has moved. The MN 500 then sends its home address and a CoA (for example, (30::10)) obtained from the access network 400 as a BU to the HA 110, to register its position in the HA (P9).
Upon receiving the BU from the MN 500, the HA 110 stores the correspondence between the home address (10::10) and the new CoA (30::10) of the MN 500 as a binding cache (P10). Thereupon, whilst the binding cache exists, the HA 110 receives packets sent to the home address (10::10) of the MN 500, by proxy, and then forwards the received packets to the CoA (30::10) of the MN 500.
Here, if the connection between the MN 500 and the access network 300 is disconnected, then the packets sent to the MN 500 until registration of a new CoA (30::10) is completed in the HA 110 will be forwarded from the HA 110 to the CoA (20::10) obtained by the MN 500 from access network 300. However, these packets will not be received ultimately by the MN 500 and hence packet loss will occur.
A second problem also arises in that there is a risk of applications being disconnected.
In other words, normally, when establishing a connection with the access network 400, as in step P7, authentication is performed to check whether or not the MN 500 is a user having the right to use the access network 400. Due to this authentication, the time required to perform steps P6 to P10 becomes longer. Consequently, an application being executed between the MN 500 and the other communicating party will be disconnected.
As a method for resolving the first and second problems, it has been conceived that, during handover, rather than attempting to connect to the access network 400 after the connection with the access network 300 has been severed, the MN 500 should perform connection with both the access network 300 and the access network 400, as illustrated in FIG. 9.
In other words, in mobile IPv6 it is possible to register a plurality of CoA. By using this, MN500 monitors the radio signals with the access network 300 and access network 400 constantly, and even before the connection with the access network 300 is severed, MN500 establishes the connection with the access network 400 immediately as soon as the connection with the access network 400 becomes possible, and the CoA of the access network 400 is previously registered in the HA 110, whereby problems, such as packet loss and disconnection of applications, and the like, can be resolved.
However, with this method, since the MN 500 monitors the radio signals from both the access network 300 and the access network 400 constantly, the battery consumption of the MN 500 is increased.
Moreover, if the access areas of the access network 300 and the access network 400 are overlapping, then this means that both access networks will be used simultaneously. Consequently, there is a risk that the connection fee charged to the user will be doubled. For example, supposing that the access networks 300 and 400 are Internet Service Providers (ISP) having IMT-2000 and radio LAN access points, then situations where the access areas are overlapping in this way are liable to occur. Moreover, the access networks also end up using resources wastefully, and hence efficiency declines.